Buttonhole stitches may be automatically produced with the prior art electronic sewing machines in response to buttonhole stitch control data stored in a memory unit mounted in the sewing machine. The buttonhole stitches include in general darning stitches for reinforcing longitudinal ends of the buttonhole and first and second series of zigzag hem stitches at opposite sides of the buttonhole. The length or stitch number of the zigzag hem stitches should be adjusted in correspondence with a size or diameter with the concerned button.
For this purpose, there has been proposed to attach to a presser bar of the sewing machine a presser foot exclusively adapted to produce buttonhole stitches. According to such presser foot, it is possible to detect the longitudinal ends of zigzag hem stitches in correspondence with the concerned button, and the stitching operation can be automatically processed by sequentially reading out stitch control data for the darning stitches and zigzag hem stitches. What is to be done by the operator is simply to attach the said presser foot, select a desired one of the buttonhole stitches and operate the sewing machine as required for starting operation at a needle point to be first stitched on the workpiece for the buttonhole stitches.
With the said presser foot, it is possible to easily and automatically produce the buttonhole stitches. Applicability of the said presser foot would, however, be limited in actual sewing operation. More particularly, since the presser foot for automatic buttonhole stitching operation has a relatively wide sole area in contact with the workpiece, it has often failed to uniformly and sufficiently exert a downwardly directing pressure onto the workpiece, especially at its peripheral edge portions and in the corner, resulting in distorted and awkward appearance of the buttonhole stitches thus produced.